When a club retires a number, it can not be worn again unless that players returns as a player or coach.

The Yankees have retired 16 uniform numbers. More than any other team. In fact they have retired every single digit except number 2 and 6. Derek Jeter wears number 2 and Joe Torre wore number 6, two more possible future retired numbers.

The Yankees have also retired number 8 twice. For Bill Dickey and Yogi Berra.

The highest number ever retired is the White Sox Carlton Fisk's number 72. He wore number 27 for the Boston Red Sox which is also retired. When he joined the White Sox, Fisk reversed his number.

Nolan Ryan is the only player to have his number retired by three teams. His number 30 was retired by the Angels and 34 by the Astros and Rangers.

There are a few numbers that clubs have not officially retired, but have taken out of circulation. The Cincinnati Reds can not retire Pete Rose's number 14 because of his lifetime ban. But they do not allow any other Reds player to wear it. Although they did allow Pete Rose, Jr. to wear it.

After Darryl Kile died in 2002, the Rockies, Astros and Cardinals removed his number 57 from circulation.

The Cardinals retired number 42 in honor of Jackie Robinson and also Bruce Sutter.

In 1997, Major League Baseball announced that number 42 would be retired from all of baseball in honor of Jackie Robinson. Players who were wearing number 42 could continue to wear it until they retired. Only the Yankees Mariano Rivera still wears it.

There is currently a movement to have Major League Baseball retire number 21 in honor of Roberto Clemente. The sentiment is that Roberto did as much to open the doors for Hispanic players as Jackie Robinson did for African Americans. Click here to visit www.retire21.org.

Here's a list of all the retired uniform numbers by Major League Club.